摘要
河道宽度调整是基岩河流系统响应构造、气候、岩性等外部扰动的重要方式之一。对祁连山东段山区基岩河流进行的水力几何学研究发现，河道宽度调整是祁连山地区基岩河流响应构造驱动的重要方式之一。位于低山带的冰沟河河道宽度向下游增加的速率明显高于位于高山带的宁缠河，河道宽度一面积回归拟合结果显示，冰沟河河道宽度一面积指数（b′）值为0．55，而宁缠河为0．46。对冰沟河和宁缠河河床基岩露头硬度进行的测量和计算显示，两条河流平均硬度值（R）分别为58．8±8．8和66．0±7．2。对比河道宽度向下游的调整变化与河床基岩露头的硬度变化，发现二者无明显相关关系，说明基岩抗蚀性不是控制河道宽度变化的主要因素。对比河道宽度的系统变化与区域差异性构造抬升速率的分布模式，发现宁缠河位于高抬升速率（高山带）地区的河段河道宽度较窄（b′≈0．44），而冰沟河位于低抬升速率（低山带）地区的河段河道宽度较宽（b′≈0．55）。因此，可以推断高山带和低山带河流河道宽度向下游增加速率的系统差异，应该是河道响应不同地貌带间差异性构造抬升的结果。此外，利用经验模型和Finnegan等的模型对冰沟河和宁缠河河道宽度进行了预测，结果显示经验模型较好地预测了河道宽度的系统变化趋势，而Finnegan等的模型则更好地体现了河道内部特征的变化和各种影响因素间的相互作用。
Increasing recognition that channel width serves as an adjustable primary feature of both alluvial and bedrock rivers has refined traditional views that changes in channel slope dominate fluvial response to variable tectonic, climatic, and lithologic conditions. Downstream adjustment of channel width is an important way that rivers response to external forcing such as varying rock uplift rates, bedrock erodibility and so on. In this paper, we analyzed downstream changes in channel width of rivers draining the eastern Qilian Mountain in an effort to explore how bedrock rivers adjust their channel hydraulic geometry characteristics in response to lithologic resistance and tectonic uplift. Our study area is located in the easternmost segment of the Qilian Mountain where topography exhibits a pronounced stepwise distribution. From the south to the north it can be divided into three different topographic zones： the high mountain zone （HMZ, 3500- 5000m）, the low mountain zone （LMZ, 2500-3200m） and the corridor plain zone （CPZ, 1500m）. This region experiences intensive differential rock uplift during Quaternary and the uplift rate in the HMZ （1.2±0.4mm/a） is approximate twice than in the LMZ （0.5±0.2mm/a）, which are caused by the activities of the major thrust fault systems including the Lenglongling, the Minle-Damaying, the Huangcheng-Shuangta and the Wuwei basin South Margin faults. Moreover, rock strength is different between the topographic zones due to the various underlying strata. Therefore, eastern Qilian Mountain region is an ideal area for our hydraulic geometry study. Our study is conducted mainly around two large bedrock rivers （ Bing Gou River and Ning Chan River） in the area. Bing Gou River is an important tributary of Jin Ta River and is about 38km in length, which originates from the HMZ and flows across the Huangcheng-Shuangta fault into the LMZ. Ning Chan River is an important tributary of Xi Ying River and is about 45km in length, which drains entirely within the HMZ and across the Huangcheng- Shuangta fault flows into the trunk stream at the topographic boundary. In the field survey, a total of ca.300 high-flow channel width data and 95 lithology data are collected along Bing Gou and Ning Chan rivers utilizing a laser rangefinder and a Schmidt hammer （N type）, respectively. All of the drainage characteristic parameters such as area, gradient, longitudinal profile are extracted from digital topographic data （SRTM） base on ArcGIS 9.3 and Matlab 2010 software platforms. Our channel width data show that the downstream adjustments of Bing Gou River and Ning Chan River exhibit a distinct difference. Bing Gou River is apparently wider than the Ning Chan River, and the width-area regressions yield that the values of index b＇ are 0.55 and O. 46, respectively. Our results suggest that downstream increasing of channel width for the LMZ channel is more rapid than the HMZ channel in this area. In addition, according to our lithology measurements, the mean Schmidt R values of Bing Gou River and Ning Chan River are 58.8±8.8 and 66.0±7.2, respectively. Comparing spatial distribution patterns of rock resistance and differential tectonic uplift with channel width adjustments along the two rivers indicates that： （1） the influence of lithologic resistance on channel width is limited and not the dominated controlling factor; （2） the systematic adjustments of channel width along Bing Gou River and Ning Chan River mainly match to the differential rock uplift rates controlled by major thrust faults; （3） width adjustment is an important way that bedrock rivers response to external tectonic forcing in the eastern Qilian Mountain. Additionally, predictions with different channel width models show that traditional width-area empirical model catches the whole developing trend of channel width downstream adjustments; by contrast, Finnegan et al. ＇s model base on formula derivation of hydraulic basic relationships emphasizes the internal changes of channel system and interactions of various factors including bed material, cross-section shape and channel slope.
出处
《第四纪研究》
CAS
CSCD
北大核心
2015年第2期453-464,共12页
Quaternary Sciences
基金
国家自然科学基金项目（批准号：41201004,41001003和91125008）和中央高校基本科研业务费专项项目（批准号：lzujbky-2012-132）共同资助
关键词
基岩河流
河道宽度
构造抬升
祁连山
bedrock river, channel width, tectonic uplift, Qilian Mountain
